Production line techniques used in the canning industry are continually being modified in order to improve the speed and efficiency of production. In the past, gravity feed conveyors used to rapidly transport empty cans between operating stations have comprised an open trackwork runways including guide rails or angle brackets in spaced apart parallel arrangement forming a caged runway for rolling cans. Such conveyors often comprise adjustable rails and brackets in order to adapt the runway for various sized cans.
By way of example, FIG. 1 illustrates, in cross section, a well known design for a section 10 of an adjustable width gravity feed can conveyor. The conveyor section 10 includes first and second parallel guide rails 12 and 14 between which are positioned a pair of carrier rails 16 forming a conveyor runway for a can 11. Spaced outward from the first guide rail 12 is a longitudinal supporting rail 18. The second guide rail 14, the carrier rails 16 and the suporting rail 18 are rigidly connected to one another along their length with assembly bolts 20 or other suitable fastening means which extend across the entire width of the conveyor section 10. Various sized spacers 22 are interposed between the rails 14, 16 and 18 to attain a desired spaced relationship.
The open trackwork of the conveyor section 10 is adjustable to accommodate various sized cans. The first guide rail 12 is extended from the supporting rail 18 by threaded adjustment bolts 24 which are welded to the guide rail 12 and passed through the support rail 18. Pairs of nuts 26 and washers 28, placed on the adjustment bolts 24 on opposing sides of the guide rail 12, in combination with helical springs 30, positioned along the bolts 24 between the washers 28 and the guide rail 12, are used to displace the bolts 24 and urge the rails 12 and 18 apart. This and other adjustment arrangements have proven awkward and inconvenient because of the time and difficulty involved when installing and adjusting rail spacings for different can sizes. In the beverage industry where cost competition is highly dependent on production rates, such arrangements are simply not cost effective.
In the past, the operating rates of conveyors for unfilled cans have generally been constrained to approximately 1,000 cans per minute. This is in part due to the relatively low structural strength of unsealed, i.e., open end, cans which permits deformation when the open end contacts a guide rail. More specifically, the can open end tends to have sharp edges which can impede can motion upon contact with one of the guide rails. If such contact occurs, sliding friction will tend to turn the can such that its axis of rolling rotation is not normal to the direction of motion. Forces exerted on that can by following cans will increase any can deformation and lead to a jam. In order to avoid this problem, early designs of low speed gravity feed can conveyors were improved upon by providing intermittent slots along the center of the conveyor runway. The slots permitted cans that were not directly aligned with the chuting to drop through the runway. These slots were formed by removing the support rails and replacing the guide rails with angle brackets which both supported and guided the rolling cans. However, with increased conveyor operating rates and weight reductions in metal beverage containers, can deformation has become more prevalent. Such deformation inhibits rolling and may prevent a deformed can from reaching a drop-out slot. It is therefore necessary to minimize transitions between runway support members in order to provide a smoother rolling path for lightweight cans. Even minor ridges and joints in the support rails 16 may have the effects of impeding the rolling speed of cans and deflecting cans from proper alignment.
Furthermore, in order to maximize runway speed, the surface to surface contact area between the rolling cans and the support rails should also be minimized. In the past, higher rolling speeds have been achieved by forming the support rails from half round rods 34 as illustrated in a simple form for two sections 36 and 38 of a gravity feed conveyor chute 40 in FIGS. 2 and 3. Further reductions in rolling resistance have been attained by covering the support and guide rails with a low friction plastic material such as ultra high molecular weight polyurethane. The chute 40 comprises several rigid rectangular collars 42 one of which is illustrated in the cross sectional view of FIG. 3. Rigid half round guide bars 46, covered with low friction plastic, are fastened along each collar sidewall and pairs of half round support bars 48 are fastened along the upper and lower inside surfaces of the bands 42.
Although conveyor designs similar to the chute 40 illustrated in FIGS. 2 and 3 are able to process up to 1,000 cans per minute, lightweight unsealed cans are especially prone to misalignment because their relatively sharp open edges catch on even the low friction plastic covering along the guide bars 46. As a result, even at relatively low process rates, e.g., less than 800 cans per minute, cans tend to misalign. Furthermore, the rectangular collars 42 may interfere with misaligned cans, sometimes preventing them from freely dropping through runway slots and causing the misaligned cans to jam up the can procession. Efforts by conveyor personnel to remove problematic cans with poles, with conduit pipe or by walking on the conveyor trackwork, often result in bending of the guiding and support rails which, in turn, further contributes to can misalignment.
Other drawbacks of conventional can conveying apparatus include the time required for installing and readjusting the rails to provide smooth runway transitions between adjacent sections of conveyor trackwork. In addition, numerous adjustment bolts along each section must be loosened and tightened in order to modify guide rail spacings when can sizes are changed. Another disadvantage of the conventional apparatus results from the relatively low structural strength of trackwork sections. This causes long runs of gravity feed conveyor chuting to sag. Extensive bracing in the form of support hangers is commonly installed to counter the large moment arms on extended chute lengths and to prevent misalignment of conveyor rails. These structural drawbacks require that substantial time be spent during conveyor set up in order to assure proper alignment. Furthermore, as a result of the extensive bracing required to support the trackwork, conventional conveyor apparatus for can processing does not possess the simple and clean appearance characteristic of good conveyor design.
Generally, prior art arrangements for gravity feed can conveyor trackwork are believed to have several limitations affecting their suitability for high speed, cost effective processing of light weight cans such as the various sized aluminum containers used by the beverage industry. In particular, it is desirable to operate gravity feed conveyors at rates which move beverage containers through processing plants at rates in excess of 1,500 cans per minute.